The invention relates to a propeller drive arrangement for vessels used in water transport, and in particular to an arrangement which incorporates a propulsion unit which can be turned in relation to the hull of the vessel. The present invention also relates to a method for moving and steering a vessel travelling on water.
In most cases, various ships or the like vessels (such as passenger ships and ferries, cargo vessels, lighters, oil tankers, ice-breakers, off-shore vessels, military vessels etc.) are moved by means of the propulsion or draw created by a rotatable propeller or several propellers. Vessels have been steered using separate rudder gear.
Traditionally, propeller operating, i.e., rotation arrangements have involved a propeller shaft drive, such as a diesel, gas or electric engine, being positioned inside the hull of the vessel, from where the propeller shaft has been taken via a duct sealed to make it watertight to outside the hull of the vessel. The propeller itself is located at the other end, i.e., the end extending outside the vessel, of the propeller shaft which is connected either directly to the engine or to a possible gearing. This solution is employed in the majority of all the vessels used in water transport in order to obtain the force required for movement.
Recently, one have also arranged for fitting vessels with propeller units in which the equipment (usually an electric motor) creating the propulsion power for the propeller shaft and any gearing are positioned outside the hull of the vessel within a special chamber or pod supported for rotating in relation to the hull. This unit can be turned in relation to the hull, which means that it can also be used for steering the vessel instead of separate rudder gear. More precisely, the pod containing the engine is supported by means of a special tubular or the like shaft to rotate in relation to the hull of the ship, which tubular shaft has been arranged through the bottom of the ship. This kind of propulsion unit is disclosed in greater detail in, inter alia, the Applicant""s FI Patent No. 76977. These units are also referred to generally as azimuthing propulsion units, and, e.g., the applicant in the present application provides azimuthing units of this kind under the trademark AZIPOD.
Besides the advantages obtained by the omitting of a long propeller shaft and separate rudder gear, this equipment has also been found to achieve a fundamental improvement in the vessel""s steerability. The vessel""s energy economy has also been found to improve. The use of azimuthing propulsion units in a variety of vessels designed for water transport has in fact become more common over the last few years, and it is assumed that their popularity will continue to grow.
In known solutions, the azimuthing propulsion unit""s turning arrangement has generally been implemented so that a geared tiller ring or the like tiller rim has been attached to the tubular shaft which forms the unit""s swivelling axis, which tiller is rotated with the aid of hydraulic engines adapted to co-operate with it. The turning movement of the tiller is also halted and kept in the halted position whenever no steering movements are performed by means of the same hydraulic engines. For this reason, there is always normal operating pressure in the hydraulic system, also when the vessel runs straight.
In accordance with one known solution, four hydraulic engines have been positioned in connection with the turning rim. The operating machinery which creates the hydraulic pressure required in the engines comprises of a hydraulic pump and of an electric motor which rotates it. In order to enhance the service reliability of the turning gear, the hydraulic engines can be arranged in two separate hydraulic circuits, each of which has its own operating machinery to create the hydraulic pressure.
A hydraulic turning system has been employed, inter alia, because hydraulics readily allow the relatively high torque required for turning an azimuthing propulsion unit to be obtained at a relatively low speed of rotation. At the same time, the turning and steering of the vessel by means of the hydraulics can be readily and relatively precisely controlled with the aid of traditional valve gears and corresponding hydraulic components. As was already stated earlier, one feature obtained with a hydraulic system has been the fact that it enables the turning movement of the propulsion unit""s shaft to be halted quickly and precisely in the desired position. This position can then be maintained, something which has been regarded as quite essential for the steering of the vessel.
However, a number of problems and deficiencies have been observed in the known hydraulic solution, which is as such found to be effective and reliable. In order to implement the turning system, the vessels have to be fitted with an expensive and complicated separate hydraulic system incorporating a large variety of components despite the fact that the rotation of the propeller itself is performed by means of an electric motor. This means, inter alia, that some of the benefit in efficiency of the use of space, obtained with the outboard azimuthing propulsion unit, is lost. Hydraulic systems also require regular and relatively frequent maintenance and inspections, which give rise to costs, and may even call for the vessel to be withdrawn from service for the duration of the maintenance work. Another deficiency of the hydraulic systems has been the fact that they have a known tendency to leak/drip oil or similar hydraulic fluid into their surroundings, in particular from hose pipes and various joints and sealing surfaces. Apart from the costs arising from the leakage and consumption of hydraulic fluid, this also causes an environmental and cleanliness problem. Leaks also cause a considerable safety risk, since surfaces stained by hydraulic fluid become slippery and thereby dangerous, and leaked hydraulic fluid may also constitute a fire risk. The hydraulic system""s internal pressure is relatively high, and thereby, e.g., a leak in a hose pipe may cause a high-pressure and often aciform (needle-shaped) jet of oil, which may cause serious injuries if it impacts with operating personnel. While it is running, the hydraulic system is also noisy, and this affects, inter alia, the operating personnel""s working conditions. The noise is continuous, since the system should be on all the time when the vessel is moving. Further, the hydraulic system achieves only a constant-speed turning movement (i.e., single-speed) for the propulsion unit. However, there are situations where a possibility for at least one other turning speed would be desirable.
The purpose of the present invention is to eliminate the deficiencies of the known technology and create a new kind of solution for turning an azimuthing propulsion unit in relation to the hull of a vessel.
One objective of the present invention is to achieve a solution which avoids the use of a separate hydraulic system and the associated problems in the turning of an azimuthing propulsion unit.
One objective of the present invention is to achieve a solution which improves the reliability and overall economy of an azimuthing propulsion unit""s turning machinery compared to the known solutions.
One objective of the present invention is to obtain a solution which reduces the noise level of an azimuthing propulsion unit""s turning machinery compared to the known solutions.
One objective of the present invention is to achieve a solution which allows the turning speed of an azimuthing propulsion unit to be altered and/or adjusted.
Another objective of the present invention is to obtain a solution which reduces the environmental risk caused by the turning machinery and improves its general level of cleanliness and safety compared to known solutions.
The invention is based on the basic insight that an azimuth propulsion unit is rotated by a direct electric drive which is controlled by a control unit that is adapted to deal with both steering commands issued for the vessel and position information provided by a sensor device which detects the position of the azimuthing propulsion unit. The operation of the electric motor is controlled by controlling the electric motor""s power supply unit using the control unit on the basis of this processing.
More precisely, the arrangement according to the present invention is characterized in particular by what is disclosed in the characterizing section of the enclosed independent claim 1. The method according to the present invention is characterized by what is disclosed in the characterizing section in the enclosed independent claim 6.
In accordance with one advantageous embodiment of the invention, the power transmission equipment which turns the azimuthing propulsion unit comprises a gear rim fitted to the shaft unit, a pinion gear, a worm, or the like adapted to co-operate with said gear rim, which gear wheel is rotated via a reduction gearing connected to an electric motor. Favorably, the equipment further comprises a suitable brake means for halting the turning of the azimuthing propulsion unit and maintaining the halted position and a functional connection between said brake means and said control unit for transferring control commands for said brake means. In accordance with one preferred embodiment the speed of rotation of the electric motor is regulated by means of an AC inverter drive.
The present invention provides several significant benefits. By means of the invention it is possible to replace the known arrangement based on the use of hydraulics, and thus the aforesaid problems associated with the use of hydraulics can be eliminated. The overall economy of a solution based on the use of an electric motor is good, and the maintenance requirement almost nonexistent. A turning system based on an electric drive is also highly reliable. In modern vessels, electricity is readily available and is employed in a number of different places (also the azimuthing propulsion unit incorporates an electric motor), and so the construction of a separate (expensive) hydraulic system is avoided. An electric drive can be used to achieve a turning arrangement with adjustable speeds for the azimuthing propulsion unit.
The present invention and its other aspects and benefits are described in greater detail in the following exemplary presentation and referring also to the attached drawing in which corresponding reference numbers in the separate Figures refer to corresponding features.